Base plate for a dual base plate heatsink

ABSTRACT

A dual base plate heatsink for use in dissipating heat for electronic devices with thermal contact between fins and the base plates and manufactured without welding. Separately extruded fins are connected to both base plates by placing the fins side by side in channels in both base plates. In order to couple the base plates and finds, the base plates are maintained at a constant relative distance and a swaging tool is passed adjacent the fins and between the base plates in a direction parallel to the surface of the base plates. The swaging tool applies pressure to the base plates to thereby swage the base plates against the ends of the fins.

This application is a divisional of U.S. application Ser. No. 11/106,440filed Apr. 25, 2005.

FIELD OF THE INVENTION

This invention relates in general to the manufacture of heatsinks, andmore specifically to a method for coupling fins in a high fin-densityheatsink to dual heat-dissipating base plates.

BACKGROUND OF THE INVENTION

Heatsinks are known in the art for receiving and then dissipating heatgenerated by electronic circuits in modern devices. Such well knownheatsinks typically comprise one base unit to which the heat generatingelectronic devices are mounted, and a plurality of fins projecting fromthe base unit for dissipating the generated heat. It is a challenge tomaximize the surface area of the fins in order to provide optimum heattransfer from the heat sink to the surrounding atmosphere while ensuringgood thermal contact between the base unit and the fins.

Heatsinks fabricated by metal extrusion have been proposed, wherein thefins and the base units are of integral construction and thereby havethe optimum thermal contact. However, as discussed in the disclosure ofU.S. Pat. No. 5,406,698 (Lipinksi), it has been shown that there arelimits to the size and shape of fins that may be made by way ofextrusion manufacturing. There has thus been proposed various methods ofmanufacturing whereby the fins are extruded separately from the baseunit, and subsequently coupled using various methods.

U.S. Pat. No. 5,771,966 (Jacoby) discloses a folded heat conductingmember or fin with at least one annealed metal insert having apredetermined thickness corresponding to a distance between the firstand second heat conductive portions of the fin and a predeterminedthickness corresponding to a depth of the groove in the base plate sothat the annealed metal insert conforms to the shape of the groove whendeformed to secure the base portion engaging region of the folded heatconducting member into the groove. The Jacoby patent proposes animpacting die to perform a deforming or swaging function to deform thefin while in the groove so that it is not removable.

U.S. Pat. No. 6,263,956 to Tang et al. sets forth a heat dissipatingstructure and method of manufacture where each slot in the base has awidth slightly less than a thickness of an inserting portion of theassociated heat dissipating fin, so that it will allow the heatdissipating fin to tightly insert therein. A fixing frame is thenmoulded into place for securing the fins. The fixing frame is formed byintroducing a melt fixing material inside of fixing recesses andthereafter cooling. As the material forms a solid, it forms the fixingframe that secures the heat dissipating fins onto the base.

Published U.S. Pat. Application No. 2002/0007936 (Woerner et al.)discloses one or more folded-fin assemblies “tacked” to the base atselected points by laser welds. In a subsequent operation, the fullsurface of the lower web portions of the folded-fin assemblies arebonded to the base, typically by brazing. According to the Woernerdisclosure, some suitable mechanical means is used to urge the lower webportions against the base prior to the laser welding, to optimize thecontact between the lower web portions and the base when the subsequentbrazing takes place. Also, a finger tool is used to maintain the desiredspacing between adjacent fins prior to laser welding, to optimize thatspacing and avoid the possibility of adjacent fins being positionedunevenly or in contact with each other. The heatsink assembly is said tobe unloaded from the laser welding apparatus and taken for brazing,soldering or other suitable bonding to the base. As an example, theheatsink assembly may receive a spray application of flux which is thenoven-dried and may be passed to a brazing furnace for heating to atemperature range of 1100-1120° F. to carry out the brazing.

Published U.S. Patent Application No. 2002/0043359 (Mizutani) sets fortha method of manufacturing a heatsink wherein fins are pressed by meansof a mould so that protrusions provided on the back side of the metalplate are pressed into “bottom-expanded recesses” to fix the heatdissipation fins and the base plate together. Mizutani teaches animpact-die mold for pressing protrusions in the base plate against thefins to keep them secure to the base plate.

Mentioned above, U.S. Pat. No. 5,406,698 (Lipinksi), proposes a heatsink manufactured by providing a baseplate with several parallel groovesin its surface. Individual fins are manufactured having a dovetail orbell-bottom at their end, the ends then being inserted into respectivegrooves. The base plate is subsequently deformed in the areas betweenthe parallel channels by rolling a plurality of coaxial rollers throughthe areas in order to crimp or swage the fins into the grooves. TheLipinski apparatus is an excellent design that requires little pressureto be transmitted though the fins themselves, so that their tendency toundesirably buckle under downward pressure is minimised. However, in theprocess of deforming the base unit in the areas between the parallelchannels, the entire base unit tends to warp. To this end, U.S. Pat. No.5,638,715 (Lipinski) sets forth an apparatus for subsequently reversingthe warp effect.

With increased consumer demand for more complex electronic systems, theneed has arisen for the more efficient use of space when manufacturingthese systems. To help meet this demand, dual base plate heatsinks havebeen proposed that are mounted to more than one electronic device butthat dissipate heat through a common set of fins. With these proposalshave come a corresponding set of challenges for manufacturing theheatsinks to specifications that promote excellent heat transfer andgood contact between the base plates and the fins. For example, theLipinksi apparatus would not be sufficient for the manufacture of dualbaseplate heatsinks because the proposed roller assembly would not bepermitted to pass through the spaces between the fins once the secondbase plate was in place.

SUMMARY OF THE INVENTION

According to the present invention, a high fin-density dual base plateheatsink is manufactured by placing fins side by side in channels formedin each of two opposing base plates. In order to couple the base platesand the fins, the relative distance between the base plates is heldconstant and a swaging tool is passed both adjacent the fins and betweenthe base plates in a direction parallel to the base plates. The pressureexerted by the swaging tool against the base plates adjacent the fins asthe base plates are held at a constant relative distance swages the baseplate adjacent each fin against the fin. Pressure is thus applied to theend of each fin inserted in each channel thereby securing the fin to thebase plate.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the preferred embodiment is set forth indetail below, with reference to the following drawings, in which:

FIG. 1 is a perspective view of a completed heatsink made according tothe preferred method of the present invention;

FIG. 2 is a perspective view of fins being mounted into a single baseplate, prior to the swaging operation according to the preferred methodof the present invention;

FIG. 3 is a partial front view of a heatsink with a swaging tool beingpassed adjacent its fins and against the base plates according to thepreferred method of the present invention;

FIG. 4 is a partial front view of a heatsink with the swaging toolhaving passed further adjacent the fins thereby having caused swaging ofthe base plates against each of the fins according to the preferredmethod of the present invention;

FIG. 5 is a cutaway partial side view of a shorter end of a tine of theswaying tool being passed adjacent a fin prior to swaging the baseplates, according to the preferred method of the present invention;

FIG. 6 is a cutaway partial side view of a taller end of a tine of theswaging tool being passed adjacent a fin and against the base plates toswage the base plates against the fin, according to the preferred methodof the present invention; and

FIG. 7 is a cutaway perspective view of the apparatus for manufacturinghigh-density heatsinks in accordance with the preferred method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

According to the present invention in its most general aspect, a dualbase plate heatsink is manufactured by providing two opposing baseplates, each with an inward facing surface and a number of elongatelanding areas separated by elongate channels. Fins are placed into thechannels of the opposing base plates and, while the base plates arebeing maintained at a constant relative distance, a swaging tool ispassed in a direction parallel to the surface adjacent the fins andbetween the base plates. As the tool is passed it increasingly appliespressure to the landing areas of the base plate adjacent the fins toswage the base plate material against the fins. The swaging of the baseplate causes pressure to be applied to the fins to force them to remaincoupled to the base plates.

With reference to FIG. 1, there is shown a dual base plate heatsink 10made according to the preferred method of the present invention. Theheatsink 10 comprises two opposing base plates 12, each base platehaving an inward-facing surface 14. Landing areas 11 of base plate 12are separated by channels 16 and comprise an elongate jaw pair 18,having jaws 20. Fins 22 have flared ends 24 that fit in between adjacentjaw pairs 18 of respective base plates 12. The channels 16 in thesurface 14 between the jaw pairs 18 receive the flared ends 24 of thefins 22. As can be seen from the diagram, the fins 22 are held in placeby jaws 20 which have been swaged towards the fins 22 to apply pressureto the flared ends 24 of the fins 22. The advantage of the flared ends24 of the fins 22 is that when the jaws 20 have been swaged, a moreuniform and secure fit is achieved for increased heat transfer.

With reference to FIG. 2, there is shown a heatsink 10 being madeaccording to the method of the present invention, wherein a fin 22 isbeing lowered into one of the channels 16 between landing areas 11 of abase plate 12. Once all of the fins 22 have been placed intocorresponding channels 16 between said jaw pairs 18, the second baseplate 12 is fit onto the flared ends 24 of the fins 22.

With reference to FIG. 3, there is shown a front view of the heatsink 10being made according to the principles of the present invention. In thisdiagram, the fins 22 have been placed into corresponding channels 16between landing areas 11 of the base plates 12, and a swaging tool 40(fully illustrated in FIG. 7) has been placed through the fins 22 andinto the space between jaws 20 in each jaw pair 18. This diagram showsclearly the flared ends 24 of the fins 22 in between jaw pairs 18.

Furthermore, the shape of each jaw 20 is shown clearly. The jaws 20progressively widen in cross section from the end distal to the surface14 of the base plate 12 towards the surface 14, and then narrow again.The base plates are maintained at a constant relative distance, asdiscussed in greater detail below with reference to FIG. 7. The wideningof the jaws 20 co-operates with the wedge shape of the swaging tool 40to progressively force the jaws 20 apart when the tines 42 of theswaging tool 40 are being passed between the respective jaws 20 in thejaw pairs 18. Furthermore, the narrowing ensures that swaging the jaws20 causes minimal warping of the base plates 12 because of a lowerbending moment.

In FIG. 4, the tines 42 of the swaging tool 40 are caused to slide in adirection parallel to the surfaces 14 of base plates 12 and between thejaws 20. Because the tines 42 of the swaging tool 40, shown more clearlyin FIGS. 5-7, are increased in height towards its second end, they pushagainst the jaws 20 of the landing area 11 to swage them apart andagainst the flared ends 24 of the fins 22. Because the base plates 12are being maintained at a constant relative distance, the jaws 20 areforced apart due to the increase in pressure from the tines 42 as theswaging tool 40 is pulled through the fins 22. The flared ends 24 of thefins 22 are pressed into channels 16 of each base plate 12 and, becausethe jaws 20 of base plates 12 have been deformed, are retained therein.

FIGS. 5 and 6 show a side cutaway view of a single tine 42 of theswaging tool 40 being passed between the base plates 12. As can be seen,the widened second end of the tine 42 pushes against both jaw pairs 18of the landing areas 11 on both base plates 12 to progressively forceopen the jaws 20 and push them against the flared ends 24 of the fin 22.

FIG. 7 shows an exemplary view of the apparatus used to form theheatsink 10 according to the present invention. The uncoupled heatsink10 is placed in a retaining structure having expansion-preventing walls50 to maintain the base plates 12 at a constant relative distance. Theswaging tool 40 is shown having multiple tines 42 that are each pulledpast the fins 22 of the heatsink 10 to force open the jaws 20 in eachjaw pair 18 of the landing area 11 so that the jaws 20 push against theflared ends 24 of the fins 22 to hold them in place in the channel 16 ofthe base plate 12.

In the embodiment of FIG. 7, the tines 42 are pulled by a shaft 54passing through a hole in each tine. The shaft is, in turn, pulled by ahydraulic motor or other motive apparatus. An alternate shaft attachmenthole 56 is shown in each of the tines 42.

Also shown in FIG. 7 are slide-preventing walls 52 which act to preventthe fins 22 from sliding relative to the base plates 12 when the tines42 of said swaging tool 40 are pulled from left to right. Theslide-preventing walls avoid the requirement set forth in U.S. Pat. No.5,406,698 to, after coupling of the fins 22 to the base plates 12,remove the parts of the fins 22 that have slid relative to the baseplates 12 during application of swaging pressure.

A person understanding the present invention may conceive ofalternatives and variations thereof. For instance, rather than employingslide-preventing walls for preventing the fins from sliding relative tothe base plates, a pressure force can be applied to both base plates toincrease the friction force between the fins and the base plates therebyreducing or prevent any relative movement. Furthermore, whereas theflared fin ends of the preferred embodiment provide a more uniform fitfor better heat transfer with the jaw pairs when swaged, uniformthickness fins can also be used.

An alternative to the smooth-sided fin shape, whether flared or not, isto provide serrations on the end of the fin to improve bonding when thebase plate material is deformed against the fin.

All such embodiments and variations are believed to be within thepurpose, sphere and scope of the invention as defined by the claimsappended hereto.

1. A base plate for receiving heatsink fins, said base plate comprising:a generally planar heat conducting base unit, said base unit having aprimary surface with a plurality of elongate, heat-conducting jaw pairsdepending from said primary surface, each of said jaw pairs separated byan elongate channel for receiving a respective end of one of said fins,each of said jaw pairs having a first jaw and a second jaw, each of saidfirst and second jaws having a side surface and an opposite sidesurface, said side surface meeting said primary surface to form anangled corner of said channel, said opposite side surface of said firstjaw facing said opposite side surface of said second jaw, each of saidopposite side surfaces shaped so that a cross section of said each ofsaid first and second jaws first progressively widens to decrease thedistance between said first jaw and said second jaw and then narrowsfrom its distal end toward the primary surface, to increase flexibilityof each of said jaws.